The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods which employ high frequency voltage to contract soft tissue structures, such as collagen connective tissue.
Collagen connective tissue can be found in many places in the human body, such as the soft tissue surrounding joints, the tissue of the cornea, the epidermal and dermal layers of the skin and the like. Collagen fibers shrink or contract when subjected to elevated temperatures, causing the caliber of the collagen fibers to increase without substantially changing the structural integrity of the connective tissue. This molecular response to temperature elevation has made contraction of collagen tissue important in many applications, such as the shrinkage of collagen tissue in the shoulder capsule or knee joint, or the collagen soft tissue in the skin in wrinkle removal procedures.
Collagen tissue is particularly important in the stability of peripheral joints, such as the shoulder, knee, hip, or the like. Peripheral joints generally comprise a covering of hyaline cartilage surrounded by a soft tissue joint capsule that maintains the constant contact of the cartilage surfaces on the ends of bones. This joint capsule also maintains the synovial fluid that provides nutrition and lubrication of the joint surfaces. Instability of peripheral joints is a significant cause of disability and functional limitation in active patients. When a joint becomes unstable, for example, its soft tissue allows for excessive motion of the joint surfaces relative to each other, and in directions not normally permitted by the ligaments or capsule. Typically, the more motion a joint demonstrates, the more inherently loose the soft tissue is surrounding the joint. If the instability is severe and recurrent, functional incapacity and arthritis may result.
Recent surgical attempts to treat joint instability have focused on tightening the soft tissue restraints that have become loose in the joints. These procedures are typically performed through open surgical approaches that often require hospitalization and prolonged rehabilitation programs. Endoscopic techniques generally cause less blood loss, have a lower risk of infection, and faster postoperative recovery times. However, arthroscopic procedures are more technically demanding than open surgical procedures because it is often difficult to access the loose tissue within the joints with endoscopic instruments.
Laser energy has been employed to effect tissue heating for contracting collagen fibers in soft tissue. For example, infrared laser energy has been used on the cornea to induce collagen shrinkage for shape modification of the cornea (laser thermokeratoplasty). In these techniques, the collagen is typically irradiated with laser coherent energy in a wavelength range of about 1.8 to about 2.55 microns to elevate the collagen temperature to about 23xc2x0 C. above normal body temperature to achieve collagen shrinkage.
Electrosurgery techniques have also been used to contract the collagen fibers in soft tissue. These techniques typically involve the application of radiofrequency (RF) energy to soft collagen tissue to contract and restrict the tissue elasticity. U.S. Pat. No. 5,458,596 to Lax, for example, describes a monopolar electrosurgical device for contracting soft tissue in which RF voltage is applied to an electrode terminal positioned near the target tissue. The electric current is caused to flow through the tissue to induce contraction of the collagen fibers. The transfer of the RF current can be through direct contact between the active electrode and the tissue, or through a thin layer of electrically conducting fluid, such as saline or gel.
Current electrosurgical devices and procedures such as the one described in Lax, however, suffer from a number of disadvantages. For example, monopolar devices generally direct electric current along a defined path from the exposed or active electrode through the patient""s body to the return electrode, which is externally attached to a suitable location on the patient. This creates the potential danger that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, the direct transfer of RF current through the target tissue tends to increase the thermal damage caused to the target tissue, and it may induce thermal damage or necrosis of body structures underlying and/or surrounding the target tissue.
For these and other reasons, improved systems and methods are desired for the electrosurgical contraction of collagen tissue.
The present invention provides systems and methods for selectively applying electrical energy to structures within or on the surface of a patient""s body. The systems and methods allow the surgical team to perform electrosurgical interventions, such as selectively contracting soft collagen tissue and other body structures, while limiting thermal damage or molecular dissociation of such tissue and limiting the thermal damage to tissue adjacent to and underlying the treatment site. The systems and methods of the present invention are particularly useful for surgical procedures in electrically conducting environments, such as arthroscopic procedures in the joints, e.g., shoulder, knee, hip, hand, foot, elbow or the like. The present invention is also useful in relatively dry environments, such as treating and shaping the cornea, and dermatological procedures involving surface tissue contraction of tissue underlying the surface of the skin for tissue rejuvenation, wrinkle removal and the like.
In one aspect of the present invention, a method for contracting soft collagen tissue involves heating an electrically conducting fluid in the region of the target site, and directing the heated electrically conducting fluid onto the target tissue to induce contraction or shrinkage of the collagen fibers in the target tissue. The electrically conducting fluid is heated to a temperature sufficient to substantially irreversibly contract the collagen fibers, which generally requires a tissue temperature in the range of about 45xc2x0 C. to 90xc2x0 C., usually about 60xc2x0 C. to 70xc2x0 C. The fluid is heated by applying high frequency electrical energy to an electrode terminal in contact with the electrically conducting fluid. The current emanating from the electrode terminal heats the fluid and generates a jet or plume of heated fluid, which is directed towards the target tissue. The heated fluid elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers.
The electrode terminal may comprise an array of electrode terminals or a single electrode at the distal end of the electrosurgical probe. In a specific embodiment, a return electrode is positioned in contact with the electrically conducting fluid to provide a current flow path from the electrode terminal(s), through the electrically conducting fluid, to the return electrode. The return electrode draws the electric current away from the tissue site to limit the depth of penetration of the current into the tissue, thereby inhibiting molecular dissociation and breakdown of the collagen tissue and minimizing or completely avoiding damage to surrounding and underlying tissue structures beyond the target tissue site. In an exemplary embodiment, the electrode terminal(s) are held away from the tissue a sufficient distance such that the RF current does not pass into the tissue at all, but rather passes through the electrically conducting fluid back to the return electrode. In this embodiment, the primary mechanism for imparting energy to the tissue is the heated fluid, rather than the electric current.
In another aspect of the invention, the electrode terminal(s) are brought into contact with, or close proximity to, the target tissue so that the electric current passes directly into the tissue to a selected depth. In this embodiment, the return electrode draws the electric current away from the tissue site to limit its depth of penetration into the tissue. Applicant has discovered that the depth of current penetration also can be varied with the electrosurgical system of the present invention by changing the frequency of the voltage applied to the electrode terminal and the return electrode. This is because the electrical impedance of tissue is known to decrease with increasing frequency due to the electrical properties of cell membranes which surround electrically conductive cellular fluid. At lower frequencies (e.g., less than 350 kHz), the higher tissue impedance, the presence of the return electrode and the electrode terminal configuration of the present invention (discussed in detail below) cause the current flux lines to penetrate less deeply resulting in a smaller depth of tissue heating. In an exemplary embodiment, an operating frequency of about 100 to 200 kHz is applied to the electrode terminal(s) to obtain shallow depths of collagen shrinkage (e.g., usually less than 1.5 mm and preferably less than 0.5 mm).
In another aspect of the invention, the size (e.g., diameter or principal dimension) of the electrode terminals employed for treating the tissue are selected according to the intended depth of tissue treatment. As described previously in copending patent application PCT International Application, U.S. National Phase Serial No. PCT/US94/05168, the depth of current penetration into tissue increases with increasing dimensions of an individual active electrode (assuming other factors remain constant, such as the frequency of the electric current, the return electrode configuration, etc.). The depth of current penetration (which refers to the depth at which the current density is sufficient to effect a change in the tissue, such as collagen shrinkage, irreversible necrosis, etc.) is on the order of the active electrode diameter for the bipolar configuration of the present invention and operating at a frequency of about 100 kHz to about 200 kHz. Accordingly, for applications requiring a smaller depth of current penetration, one or more electrode terminals of smaller dimensions would be selected. Conversely, for applications requiring a greater depth of current penetration, one or more electrode terminals of larger dimensions would be selected.
The electrically conducting fluid may be delivered to the target site before or during the surgical procedure. In relatively dry environments, for example, the fluid is delivered along a fluid path past the electrode terminal and the return electrode to the target site to generate the current flow path between the return electrode and the electrode terminal. In other procedures, such as arthroscopic procedures, the electrically conductive fluid is delivered into the arthroscopic cavity to immerse the target site in the fluid. The return electrode is then positioned within the cavity either by introducing the surgical instrument into the cavity or introducing a separate instrument. In an exemplary embodiment, a supplementary lumen is incorporated into the electrosurgical probe to direct a jet of electrically conductive fluid past the electrode(s) to effect a more defined zone of heating on the target tissue surface.
In another aspect of the invention, a method is provided for contracting or shrinking the collagen fibers within a joint capsular tissue, such as the shoulder, knee, hip, hand, foot, elbow or the like, to eliminate capsular redundancy or to otherwise tighten the ligamous complex. In this method, one or more electrode terminal(s) are percutaneously introduced through a portal in the joint and positioned adjacent to the joint capsular tissue. The cavity surrounding the joint is immersed in electrically conducting fluid, such as isotonic saline, and a return electrode is positioned within the electrically conducting fluid. A high frequency voltage difference is applied between the electrode terminal and the return electrode to locally heat the electrically conductive fluid and/or the target tissue adjacent the electrode terminal. In one embodiment, the heated fluid is propelled towards the capsular tissue to induce a contraction of the collagen fibers. In other embodiments, the electrode terminal(s) are brought into contact with, or close proximity to, the capsular tissue to pass RF current directly into the tissue to induce the collagen contraction. In both embodiments, the electric current is drawn proximally towards the return electrode to minimize unnecessary thermal damage to the capsular tissue and to the surrounding and underlying body structures.
In another aspect of the invention, a surgical instrument is provided for applying high frequency energy to tissue at a target site. The instrument includes a shaft and an electrically insulating support at or near the distal end of the shaft. An electrode array of at least three electrode terminals is embedded within the electrically insulating support such that the electrode terminals are substantially flush with the tissue treatment surface of the electrically insulating support. This configuration (i.e., flush electrode terminals) provides a more uniform heating of the fluid, and minimizes high density electric fields that may otherwise form near the edges of electrode terminals. Therefore, sufficient voltage can be applied to the electrode terminals to produce the thermal effects necessary for tissue contraction, while minimizing ablation or dissociation of tissue at or around the target site.
In yet another aspect of the invention, a system is provided for applying high frequency electrical energy to tissue at a target site. The system includes an electrosurgical probe with a shaft and at least one electrode terminal at or near the distal end of the shaft, and a fluid delivery element for delivering electrically conductive fluid to the target site. The system further includes a return electrode spaced from the electrode terminal and an electrosurgical power supply for applying high frequency voltage to the electrode terminal and the return electrode that is sufficient to cause a contraction of collagen fibers within the soft tissue. The return electrode is preferably positioned to induce a substantial portion of the electric current from the electrode terminal away from the tissue at the target site to minimize the depth of current flow into the tissue. The active electrode or electrode terminal is preferably disposed at or near the distal end of the probe and the return electrode is spaced from the active electrode and preferably enclosed within an insulating sheath. This minimizes exposure of the return electrode to surrounding tissue and minimizes possible shorting of the current between the active and return electrodes.
The system may optionally include a temperature controller coupled to one or more temperature sensors at or near the distal end of the probe. The controller adjusts the output voltage of the power supply in response to a temperature set point and the measured temperature value. The temperature sensor may be, for example, a thermocouple, located in the insulating support that measures a temperature at the distal end of the probe. In this embodiment, the temperature set point will preferably be one that corresponds to a tissue temperature that results in the contraction of the collagen tissue, i.e., about 60xc2x0 C. to 70xc2x0 C. Alternatively, the temperature sensor may directly measure the tissue temperature (e.g., infrared sensor). This embodiment is advantageous in situations when the surgeon is moving the probe transversely across the tissue.